Tests to detect food allergies in children could be missing many potentially life-threatening conditions, experts have warned.

For every child diagnosed with an allergy via blood or skin prick tests, another goes undiagnosed, a recent study has cautioned.

Dr Kate Grimshaw, a specialist paediatric dietitian at Southampton Children's Hospital, said not all allergies can be detected by measuring levels of immunoglobulin E (IgE) antibody, which is linked to allergic reactions.

Her advice comes as new research into cow's milk allergy found for every UK child who had a cow's milk reaction due to IgE in their blood, there was a child who suffered a reaction, who did not.

Blood tests to detect allergies could be missing many potentially life-threatening conditions in children

The study was published online in the medical journal Allergy.

Dr Grimshaw, who was involved in the European Union funded project known as EuroPrevall, said: 'We know that sometimes if a child is seen for a possible food allergic reaction - to any food, not just milk - but tests show there is no measurable IgE, then a possible food reaction may be ruled out, when in fact the child may be reacting to the food, just not via IgE.

'This research will hopefully highlight to GPs and non-allergy specialists that just because an IgE test is negative, the child may in fact be reacting to a food and further investigations should be carried out.'

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The first is IgE-mediated, and cause a range of immediate symptoms such as skin rashes, vomiting, respiratory issues and, in some cases, potentially life-threatening reactions.

Meanwhile, non IgE-mediated reactions occur around four to 28 hours after an incident and may cause stomach complaints such as diarrhoea or constipation, among other problems.

The study, which saw more than 9,000 babies from nine European countries followed up until the age of two, found that 1.3 per cent of UK children reacted to milk within two hours - the highest rate of all countries involved.

Meanwhile, only just under half (45 per cent) had IgE at a level deemed likely to cause symptoms.

A study found that for every child diagnosed with an allergy to cow's milk following a test measuring levels of immunoglobulin E (IgE), which is linked to allergic reactions, another child's allergy is missed because their test comes back negative (picture posed by a model)

Professor Graham Roberts, a consultant in paediatric allergy and respiratory medicine at Southampton Children's Hospital, and principal investigator for the UK study, said: 'Our study shows that a significant number of children can be reacting to a food despite having a negative IgE test.

'The take-away message for any non-allergy specialist is, if the patient's history is convincing, then further investigations should be made if IgE tests are negative to ensure the child isn't actually reacting to a food.'

The research, funded in the UK by the Food Standards Agency, was part of a project locally called Prevalence of Infant Food Allergy, which assessed the development of food allergies in children in Hampshire in the first two years of life.

Dr Grimshaw and Professor Roberts now plan to reassess all 1,140 children who participated in that research at school age to discover what happens to allergies that started in early childhood and find out which older children develop allergies and asthma.